[adydula]

I have one set for unity gain and 2.5x the other is 2.5/6.5 etc....with all my cans the unity gain drives them very very loud...
 
LCD2, Q701, Grado 325is, Beyer 1350, Beyer T90 etc
 
A.

 

[exquisite]

Thanks for the answers. The question was specifically related to the EHP-O2 unit - this one : 
 
 http://epiphany-acoustics.co.uk/products-page/dacs/ehp-o2d-miniature-desktop-headphone-amplifier-with-usb-dac/
 
 So far I have 2 users(owners) saying it´s 2,5X/6,5X and the manufacturer (backed up by another user) saying it´s 1X/5X . 
 
PS: never asked about loudness levels, just about manufacturing specs. It´s a shame this is not listed on vendor´s page.

 

[Ashade]

I understand that. I was giving you a reference for you to get an idea and being able to try to identify your gain. The other option you have is open it and have a look to the actual resistances. That way you can get the gain values.

 

[adydula]

Send them a note and ask them?
 
The gain is really an easy thing to change etc...done this on an amp..simple cut and end of two resistors etc...
 
A.

 

[MrEleventy]

The original designer of the O2 has it set at default, 2.5x/6.5x. Since it's a DIY kit, you can change it to whatever you wish. If Epiphany built it to exactly as NW intended, then it's 2.5/6.5. If they say they changed it, it's whatever they changed it to. If the site says 1/5, then it's 1 and 5.

 

[Ashade]

Which is something I'm considering for my next build because I never use 6.5x. 2.5x is already excessively loud.

I'm considering either 1x/2.5x or 1x/5x

 

[adydula]

Again, this is really not an issue...very easy to adjust etc...
 
A.

 

[agdr]

   
I would buy a complete unit w/ integrated ODAC in an instant if it was available, I don't trust my soldering skills heh. How long have you been testing it?
 
Does this version increase the requirements for lower end headphones?

 
I've had one playing continuously 24/7 for at least a month now.  The amp will power the same range of headphones that the O2 amp will, plus hard-to-drive phones that require a lot more current and/or more voltage.  320mA per channel vs. about 120mA per channel for the O2, and 10.5Vdc (rms) output swing with +/-16Vdc supplies vs. 7Vdc (rms) with the +/-12Vdc supplies in the O2.
 
A few folks out there are in the process of building the amps (past PC board run).  Maybe someone will eventually put a finished one up for sale.

 
 

  I was actually thinking of building this but the pc boards have a minumum order and it gets pricey...unless u can get a bunch of people to help finance etc..
 
Alex

 

Alex - I am probably going to do another at-cost board run in a few weeks.  I'll send you a PM. I'll find out where the appropriate place to post about that is over here, probably in the DIY section.  Yeah, that 5 board minimum for the 4-layer PC board fab at Seeed Studio is a big hurdle for the DIY effort.  Folks only need 1 board, or 2 if built up in the B4-160 case with the power supply and ODAC on the back board.

 

[adydula]

agdr,
 
Thanks for this information, I sent you a PM.
 
Your one of the few people that I respect when it comes to an honest enginering design discussion about the O2.
 
I will sign up for one board and a hardware kit....but you have me thinking of the all in one amp with the ODAC inside...just one more board...
 
hmmm
 
Alex

 

[agdr]

  I will sign up for one board and a hardware kit....but you have me thinking of the all in one amp with the ODAC inside...just one more board...

 
That two board option really is an interesting way to go.  The B4-160 case, which is twice as long, is just $5 more at Allied Electronics or Newark with about the same shipping cost.  Same parts, the power supply parts just go on the back board along with an ODAC.  An ODAC would still mount in the single board B4-080 option, bolted upside down onto a blank board slid into the upper slot of the case.
 
I should say that I've decided to work on a version 2.0 with a few additions.  I'll need to build it and test it again so the boards for that likely won't be out for several months, maybe even next year.  In the meantime the current version at the google link works fine.
 

 
@agdr
Wow. You've done an incredible amount of work on that, it's very impressive. Definitely adds some good features to the minimal O2 design. I've always felt the O2 is somehow just 'not quite right'. It seems conflicted whether to be a portable or desktop rig. I have no interest in portable audiophilia beyond good buds, and I'm sure most people are using the O2 as a desktop solution.
 
In my opinion the front AC plug, the unnecessary battery circuit and the lack of current (to preserve battery, as mentioned by another member) are problems. I am interested in building an amp that deals with these as efficiently as possible. But circuitry diagrams are scary 

. 

 
Hey thanks.  Sorry about the delayed reply, I hadn't circled back yet after posting. 
 
I'm a fan of the O2 and have posted several modifications to it elsewhere over the last couple of years since the O2 was released.  That size issue was kind of the one big hiccup right out of the gate though, IMHO.  The O2 was a little too large to be in the truely "portable" DIY headamp category, like AMB's mini^3 which I'm pretty sure was one of the things NwAvGuy intended it to compete against, but too small to include desktop things like RCA and 1/4" jacks, at least not in the B2 case.  That stuff can fit in the B3 case of course, and I know that several of the O2 builders out there offer that mod.
 
I was eager to ditch the O2's power management circuit for an actual anti-thump time-delay relay in the desktop amp.

 

[Currawong]

Alex - I am probably going to do another at-cost board run in a few weeks.  I'll send you a PM. I'll find out where the appropriate place to post about that is over here, probably in the DIY section.  Yeah, that 5 board minimum for the 4-layer PC board fab at Seeed Studio is a big hurdle for the DIY effort.  Folks only need 1 board, or 2 if built up in the B4-160 case with the power supply and ODAC on the back board.

 
I remember the DIY Audio board run for O2s was huge. If you can PM me (or another mod) prior to posting in the DIY forum about it, I'd appreciate it. Due to issues in the past, group buys are restricted to DIY items, with permission.
 
Just an FYI for everyone: If anyone plans on building for the purpose of selling them, then that person (or people) if they are members here, have to PM Jude or myself to register as a Member of the Trade (which means you get a tag under your name). That is explained in the rules. One O2 builder refused to abide by the rules and was banned, so I really want to make sure people are aware of this in advance so that doesn't become a problem again.  

 

[bada bing]

I jumped the gun on a ODA PCB group buy and made an order for 10 ( in white

).
It isn't a cheap amp to build, with all options, my total parts were ~$250 for 1.
It appears to go a long ways towards eliminating the weaknesses of the original
O2 for desktop use IMO.
 
The PSU section on the PCB is useful. I'm thinking of using the PSU section
of one of the boards to power a populated dynalo board I have sitting unused.
I like the idea of a one box amp build with the transformer located at the wall.
Should make for a nice compact desktop footprint with the benefit of the isolation
from the transformer.
 
Thank you very much adgr for publishing the exceptional documentation on the
project. It is appreciated. I'll definitely ask for a couple boards of your next revision
when the time comes.

 

[dclaz]

The O2/ODAC all in 1 combo isn't suited for outputting to amplified speakers right? I may have to grab the ODAC now and the O2 down the road when I buy some nice headphones.
 
Is it reasonable to say the O2 will drive any set of cans you throw at it? HD800's LCD2's etc?

 

[Ashade]

That's what the designer states. I'm pretty sure it can, it is a pretty powerful amp.

 

[ProTofik]

Hd800 are driven by o2 without a problem. Not sure about the lcd2 through